From Italian patent application No. 20,322 A/86 it is known the use of fluid perfluoropolyethers endowed with a kinematic viscosity ranging from 8,000 to 40,000 cSt at 20.degree. C.--as lubricating oils or components of perfluorinated lubricating greases in order to obtain lubricants having a low friction coefficient.
In said patent application it is proved that it is not possible to obtain a low friction coefficient from perfluoropolyethers of the straight type endowed with a low kinematic viscosity, for example of 30-250 cSt.
On the other hand it is found that the antiwear properties of a perfluoropolyether cannot be directly correlated to the friction coefficient, as such properties do not improve as the viscosity increases.
Furthermore, from Italian patent application No. 20,159 A/86 there are known several additives for lubricants based on perfluoropolyether compounds, which impart antirust properties to said perfluoropolyethers.
Also in such case these additives seem not to impart particular antiwear properties to the perfluoropolyether lubricants, thereby proving that such properties cannot be directly correlated to the antirust properties.
On the other hand, the antiwear characteristics of the perfluoropolyether lubricants are similar to the ones of the mineral oils and not fully satisfactory for most of the practical applications of the lubricants.